Wheel unit

ABSTRACT

A wheel unit includes a motor, a pinion gear fixed to a rotating portion of the motor, a wheel including an annular ground surface and rotating around a final gear support shaft, and a final gear disposed on one side in an axial direction with respect to the wheel. The wheel unit further includes a speed reduction mechanism which decelerates rotation of the pinion gear and transmits the rotation to the final gear and a gear case which accommodates the pinion gear. When viewed from the axial direction, the final gear support shaft and the motor shaft are disposed in different positions. An initial stage composite gear of the speed reduction mechanism meshes with the pinion gear. The initial stage composite gear is supported by the final gear support shaft such that the initial stage composite gear and the final gear are rotatable relative to the gear case.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wheel unit.

2. Description of the Related Art

In a self-propelled electric appliance such as a cleaning robot, a wheelunit including a wheel and a motor that drives the wheel is mounted. Forexample, on the left and the right of an autonomous floor-cleaning robot10 disclosed in Japanese Unexamined Patent Application Publication No.2004-195215, main wheel subassemblies 42A and 42B are mounted. The mainwheel subassembly of the related art includes wheels 42AW and 42BWattached to be rotatable and motors 42AM and 42BM which operate to drivethe respective wheels (see, for example, paragraphs [0018] to [0021] andFIGS. 4 and 5 of Japanese Unexamined Patent Application Publication No.2004-195215).

Hitherto, in this type of cleaning robot, a motor with a brush havinglarge dimensions in an axial direction is used. When the motor and thewheel are arranged to be aligned in the axial direction, the dimensionsof the wheel unit in the axial direction are increased. Therefore, inthe related art, the motor is disposed on the outside of a groundsurface of the wheel to reduce the dimensions of the wheel unit in theaxial direction. Also in FIG. 4 of Japanese Unexamined PatentApplication Publication No. 2004-195215, a state where the motors 42AMand 42BM are arranged on the outside of the ground surface of the wheelis illustrated.

However, when the motor is disposed on the outside of the ground surfaceof the wheel, the wheel unit is increased in size in a movementdirection or a vertical direction. Therefore, the degree of freedom fora design of other parts of the cleaning robot is reduced. Therefore,there is a demand for a reduction in the dimensions of the wheel unit inthe axial direction without an extension of the wheel unit in themovement direction or the vertical direction.

In contrast, in the wheel unit, a support structure for rotatablysupporting a gear or the wheel is included. When the reduction in thesize of the wheel unit is taken into consideration, there is a need tosufficiently ensure the durability of the support structure.

SUMMARY OF THE INVENTION

According to a first preferred embodiment of the present invention, awheel unit includes: a motor including a motor shaft; a pinion gearwhich is fixed to a rotating portion of the motor; a wheel whichincludes an annular ground surface and rotates around a final gearsupport shaft; a final gear made of a resin, which is fixed to the wheeldirectly or via another member and is disposed on one side in an axialdirection with respect to the wheel; a speed reduction mechanism whichdecelerates rotation of the pinion gear and transmits the rotation tothe final gear; a gear case which accommodates the pinion gear, thespeed reduction mechanism, and the final gear; and a rotation supportportion which rotates along with the final gear and the wheel whilebeing supported by the gear case directly or via another member and isprovided between the final gear and the wheel; wherein when viewed fromone side in the axial direction, the final gear support shaft and themotor shaft are disposed in different positions; the motor includes arotor magnet on an outside of an armature in a radial direction; atleast a portion of the final gear is positioned on an inside of acylindrical or substantially cylindrical area surrounded by the groundsurface; and the speed reduction mechanism includes a plurality ofcomposite gears each including a large-diameter gear portion and asmall-diameter gear portion; an initial stage composite gear is disposedon the one side of the final gear in the axial direction, thelarge-diameter gear portion of the initial stage composite gear mesheswith the pinion gear; the initial stage composite gear is supported bythe final gear support shaft; and the initial stage composite gear andthe final gear are rotatable relative to the gear case.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a wheel unit according to a first preferredembodiment of the present invention, which is partially cut-away forillustration purposes.

FIG. 2 is a perspective view of a wheel unit according to a secondpreferred embodiment of the present invention.

FIG. 3 is a side view of the wheel unit according to the secondpreferred embodiment of the present invention.

FIG. 4 is an exploded perspective view of the wheel unit according tothe second preferred embodiment of the present invention.

FIG. 5 is a front view of the wheel unit according to the secondpreferred embodiment of the present invention, which is partiallycut-away for illustration purposes.

FIG. 6 is a side view of the wheel unit according to the secondpreferred embodiment of the present invention, which is partiallycut-away for illustration purposes.

FIG. 7 is a side view of a wheel unit according to a third preferredembodiment of the present invention.

FIG. 8 is a side view of the wheel unit according to the third preferredembodiment of the present invention, which is partially cut-away forillustration purposes.

FIG. 9 is a side view of the wheel unit according to the third preferredembodiment of the present invention, which is attached to a cleaningrobot.

FIG. 10 is a side view of the wheel unit according to the thirdpreferred embodiment of the present invention, which is attached to thecleaning robot.

FIG. 11 is a perspective view of a wheel unit according to a modifiedexample of a preferred embodiment of the present invention.

FIG. 12 is a side view of a wheel unit according to a fourth preferredembodiment of the present invention.

FIG. 13 is a cross-sectional view of the wheel unit according to thefourth preferred embodiment of the present invention, which is partiallycut-away for illustration purposes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, exemplary preferred embodiments of the present inventionwill be described with reference to the drawings. In addition, in thefollowing description, a direction along a final gear support shaft isreferred to as an “axial direction”. In addition, along the axialdirection, a motor side is referred to as an “input side”, and a wheelside is referred to as an “output side”.

First Preferred Embodiment

FIG. 1 is a front view of a wheel unit 1A according to a first preferredembodiment of the present invention. FIG. 1 illustrates a wheel 6A and agear case 7A, which are cut-away for illustration purposes. Asillustrated in FIG. 1, the wheel unit 1A preferably includes a motor 2A,a pinion gear 3A, a speed reduction mechanism 4A, a final gear 5A, thewheel 6A, and the gear case 7A. The pinion gear 3A is fixed to arotating portion of the motor 2A. The speed reduction mechanism 4Adecelerates rotation of the pinion gear 3A and transmits the rotation tothe final gear 5A. The final gear 5A is preferably fixed to the wheel 6Adirectly or via another member. The wheel 6A preferably includes anannular ground surface 621A, and rotates about the final gear supportshaft 51A. The pinion gear 3A, the speed reduction mechanism 4A, and thefinal gear 5A are preferably accommodated in an inner portion of thegear case 7A.

In addition, a rotation support portion 81A is preferably providedbetween the final gear 5A and the wheel 6A. The rotation support portion81A rotates along with the final gear 5A and the wheel 6A while beingsupported by the gear case 7A.

As illustrated in FIG. 1, in the wheel unit 1A, the entire final gear 5Ais positioned on the inside of a cylindrical or substantiallycylindrical area surrounded by the ground surface 621A. However, only aportion of the final gear 5A may be positioned on the inside of thecylindrical or substantially cylindrical area surrounded by the groundsurface 621A. Accordingly, compared to a case where the final gear 5A isdisposed on the outside of the wheel 6A, the dimensions of the wheelunit 1A in the axial direction are reduced.

On the other hand, in this structure, it is difficult for a supportstructure of the rotation support portion 81A with respect to the gearcase 7A to be widened in the axial direction. In the wheel unit 1A, anoutside diameter of the rotation support portion 81A is larger than anoutside diameter of the final gear support shaft 51A. Accordingly, alarge contact portion of the gear case 7A and the rotation supportportion 81A is ensured. As a result, the durability of the supportstructure of the rotation support portion 81A with respect to the gearcase 7A is enhanced. Second Preferred Embodiment

FIG. 2 is a perspective view of a wheel unit 1 according to a secondpreferred embodiment of the present invention. FIG. 3 is a side view ofthe wheel unit 1 when viewed from the input side. FIG. 4 is an explodedperspective view of the wheel unit 1.

The wheel unit 1 is preferably mounted, for example, in a self-propelledcleaning robot which is a domestic electric appliance, and is preferablyused as a unit that allows the cleaning robot to travel. As illustratedin FIGS. 2 to 4, the wheel unit 1 of this preferred embodimentpreferably includes a motor 2, a pinion gear 3, a speed reductionmechanism 4, a final gear 5, a wheel 6, and a gear case 7. When themotor 2 is driven, drive force of the motor 2 is transmitted to thewheel 6 via the pinion gear 3, the speed reduction mechanism 4, and thefinal gear 5. Accordingly, the wheel 6 rotates.

In the motor 2 of this preferred embodiment, a brushless DC motor ispreferably used, however, any other desirable type of motor could beused. The motor 2 preferably includes a stationary portion 21 which isfixed to the gear case and a rotating portion 22 which rotates relativeto the stationary portion 21. As indicated by broken dashed line in FIG.3, the stationary portion 21 preferably includes an armature 211 definedby a stator core and coils. On the other hand, the rotating portion 22preferably includes an annular magnet 221. When drive current flowsthrough the coils of the armature 211, a magnetic flux is generated inthe stator core. In addition, the rotating portion 22 is rotated bymagnetic action between the armature 211 and the magnet 221.

The motor 2 of this preferred embodiment is preferably a so-called outerrotor type motor in which the magnet 221 is disposed on the outside ofthe armature 211. In the outer rotor type motor, a magnet having alarger diameter than that of an inner rotor type motor can be used.Therefore, while an increase in the dimensions of the magnet in theaxial direction is avoided as much as possible, high output is obtained.Accordingly, when the outer rotor type motor is used, the dimensions ofthe motor 2 in the axial direction are reduced. Otherwise, even in acase where the volume of the magnet is further increased to increase theoutput, the increase in the dimensions in the axial direction isprevented or significantly reduced. For example, the dimensions of themotor 2 in the axial direction is preferably smaller than the diameterof the rotating portion 22 of the motor 2. As a result, when viewed inthe axial direction, a small wheel unit 1 is provided.

Subsequently, the inner structure of the gear case 7 will be described.FIG. 5 is a front view of the wheel unit 1, in which the wheel 6 and thegear case 7 are cut-away for illustration purposes. FIG. 6 is a sideview of the wheel unit 1, in which the gear case 7 is cut away forillustration purposes. As illustrated in FIGS. 4 to 6, in the innerportion of the gear case 7, the pinion gear 3, the speed reductionmechanism 4, and the final gear 5 are arranged.

The rotating portion 22 of the motor 2 rotates along with a motor shaft222 which extends in the axial direction. An end portion of the motorshaft 222 on the output side extends to the inner portion of the gearcase 7. In addition, the pinion gear 3 is preferably fixed to the endportion of the motor shaft 222. The pinion gear 3 is preferably made ofa resin material such as, for example, a POM (polyacetal) or a metal.The pinion gear 3 includes a plurality of teeth which mesh with a firstlarge-diameter gear portion 412, which will be described later.

The speed reduction mechanism 4 preferably includes a first compositegear 41, a second composite gear 42, and a third composite gear 43. Thefirst composite gear 41 is rotatably supported by a first support shaft411 which extends in the axial direction. The second composite gear 42is preferably rotatably supported by a second support shaft 421 whichextends in the axial direction. The third composite gear 43 ispreferably rotatably supported by a third support shaft 431 whichextends in the axial direction. All of the first support shaft 411, thesecond support shaft 421, and the third support shaft 431 are fixed tothe gear case 7 so as not to rotate.

The first composite gear 41 preferably includes the first large-diametergear portion 412 and a first small-diameter gear portion 413 which ispositioned closer to the output side than the first large-diameter gearportion 412 and has a smaller diameter than that of the firstlarge-diameter gear portion 412. The first large-diameter gear portion412 rotates while a plurality of teeth thereof mesh with a plurality ofteeth of the pinion gear 3. However, the number of teeth of the firstlarge-diameter gear portion 412 is preferably greater than the number ofteeth of the pinion gear 3. Therefore, the first composite gear 41rotates at a lower rotation frequency than the pinion gear 3.

The second composite gear 42 preferably includes a second large-diametergear portion 422 and a second small-diameter gear portion 423 which ispositioned closer to the output side than the second large-diameter gearportion 422 and has a smaller diameter than that of the secondlarge-diameter gear portion 422. The second large-diameter gear portion422 rotates while a plurality of teeth thereof mesh with a plurality ofteeth of the first small-diameter gear portion 413. However, the numberof teeth of the second large-diameter gear portion 422 is preferablygreater than the number of teeth of the first small-diameter gearportion 413. Therefore, the second composite gear 42 rotates at a lowerrotation frequency than the first composite gear 41.

The third composite gear 43 preferably includes a third large-diametergear portion 432 and a third small-diameter gear portion 433 which ispositioned closer to the output side than the third large-diameter gearportion 432 and has a smaller diameter than that of the thirdlarge-diameter gear portion 432. The third large-diameter gear portion432 rotates while a plurality of teeth thereof mesh with a plurality ofteeth of the second small-diameter gear portion 423. However, the numberof teeth of the third large-diameter gear portion 432 is preferablygreater than the number of teeth of the second small-diameter gearportion 423. Therefore, the third composite gear 43 rotates at a lowerrotation frequency than the second composite gear 42.

The final gear 5 is preferably rotatably supported by a final gearsupport shaft 51 which extends in the axial direction. The final gearsupport shaft 51 is fixed to the gear case 7 so as not to rotate. Thefinal gear 5 rotates while a plurality of teeth thereof mesh with aplurality of teeth of the third small-diameter gear portion 433.However, the number of teeth of the final gear 5 is preferably greaterthan the number of teeth of the third small-diameter gear portion 433.Therefore, the final gear 5 rotates at a lower rotation frequency thanthe third composite gear 43.

In this manner, the drive force of the motor 2 is transmitted from thepinion gear 3 to the final gear 5 via the first composite gear 41, thesecond composite gear 42, and the third composite gear 43. As describedabove, the rotation frequency is reduced through the plurality of gears.On the other hand, torque is increased through the plurality of gears.

That is, the speed reduction mechanism 4 plays a role of reducing therotation frequency and transmitting power from the pinion gear 3 to thefinal gear 5 while increasing the torque.

The first composite gear 41, the second composite gear 42, the thirdcomposite gear 43, and the final gear 5 are preferably made of, forexample, a resin such as POM (polyacetal). However, the first compositegear 41, the second composite gear 42, and the third composite gear 43may alternatively be made of a metal if so desired.

At a position of the final gear 5 adjacent to the output side, arotation support portion 81 which rotates while being supported by thegear case 7 is preferably provided. The rotation support portion 81 ispositioned between the final gear 5 and a wheel portion 61, which willbe described later, and is supported by a circular hole portion 70provided in a side wall of the gear case 7. The rotation support portion81 has a cylindrical outer peripheral surface which is disposedcoaxially or substantially coaxially with the final gear support shaft51. The rotation support portion 81 rotates while the outer peripheralsurface thereof comes into contact with an edge of the circular holeportion 70 of the gear case 7. That is, in this preferred embodiment, aslide bearing is configured by the outer peripheral surface of therotation support portion 81 and the circular hole portion 70 of the gearcase 7. Between the outer peripheral surface of the rotation supportportion 81 and the circular hole portion 70 of the gear case 7, alubricant such as, for example, a grease may be interposed.

In addition, at a position of the rotation support portion 81 adjacentto the output side, a polygonal column-shaped key portion 82 whichextends in the axial direction is provided. In this preferredembodiment, the final gear 5, the rotation support portion 81, and thekey portion 82 are preferably defined by a single monolithic moldedproduct made of a resin such as POM (polyacetal). Accordingly, thenumber of components is reduced, and thus assembly of the wheel unit 1is facilitated. However, the final gear, the rotation support portion,and the key portion may alternatively be prepared as separate members tobe fixed to each other, if so desired.

The wheel 6 preferably includes the wheel portion 61 made of, forexample, a resin or a metal and a tire portion 62 made of, for example,a rubber or a resin other than the rubber. The wheel portion 61 extendsin a radial direction with respect to the final gear support shaft 51.The tire portion 62 is fixed to the outer peripheral portion of thewheel portion 61. The tire portion 62 preferably includes an annularground surface 621 which has a constant or substantially constant width.At the center of the wheel portion 61, a key groove 611 which is opentoward the input side is provided. The key portion 82 is fitted into thekey groove 611 to be fixed. Accordingly, when the final gear 5 rotates,the rotation support portion 81, the key portion 82, the wheel portion61, and the tire portion 62 integrally rotate about the final gearsupport shaft 51.

As illustrated in FIG. 5, the wheel portion 61 of the wheel 6 isprovided in or substantially in a cup shape which is open toward theinput side. Therefore, a surface of the wheel portion 61 on the inputside is a recessed surface which is further recessed toward the outputside than an end portion of the tire portion 62 on the input side. Inaddition, in the inner portion of the wheel portion 61, the final gear 5is preferably partially accommodated. That is, in this preferredembodiment, a portion of the final gear 5 is positioned on the inside ofthe cylindrical or substantially cylindrical area surrounded by theground surface 621 of the wheel 6. Accordingly, the end portion of thefinal gear 5 on the output side is positioned closer to the output sidethan the end portion of the tire portion 62 on the input side. In thiscase, the dimensions of the wheel unit 1 in the axial direction becomesmaller than those in a case where the entire final gear 5 is disposedon the outside of the wheel 6.

In addition, in this preferred embodiment, when the wheel unit 1 isviewed in the axial direction as illustrated in FIG. 6, all of thepinion gear 3, the three composite gears 41 to 43, and the final gear 5are preferably arranged on the inside of the ground surface 621 of thewheel 6. That is, on the inside of the cylindrical surface on which theground surface 621 of the wheel 6 is projected in the axial direction,the pinion gear 3, the three composite gears 41 to 43, and the finalgear 5 are arranged. Accordingly, in a direction orthogonal to the axialdirection, the area occupied by the wheel unit 1 is reduced.

In addition, as illustrated in FIG. 6, in this preferred embodiment, thefirst support shaft 411 that supports the first composite gear 41, thesecond support shaft 421 that supports the second composite gear 42, andthe third support shaft 431 that supports the third composite gear 43are arranged about the final gear support shaft 51 in a circumferentialor substantially circumferential direction. The three composite gears 41to 43 are preferably arranged in a spiral pattern about the final gearsupport shaft 51. In this arrangement, the plurality of gears arecompactly arranged while also preventing each gear from coming intocontact with the support shafts of the other gears.

In addition, as illustrated in FIG. 6, in this preferred embodiment, anangle q 1 between the first support shaft 411 and the second supportshaft 421 with respect to the final gear support shaft 51 and an angle q2 between the second support shaft 421 and the third support shaft 431with respect to the final gear support shaft 51 are preferably about 90°or less. Accordingly, all of the three composite gears 41 to 43 can bearranged at positions biased toward one direction with respect to thefinal gear 5. In this preferred embodiment, all of the three compositegears 41 to 43 are arranged at higher positions than the final gear 5.As a result, the arrangement of the plurality of gears becomes morecompact.

When the wheel unit 1 mounted in a cleaning robot is reduced in size,the degree of freedom for a design of parts of the cleaning robot isincreased. For example, by using a lager battery, dust box, or suctionblower in the cleaning robot, the performance of the cleaning robot canbe improved. In addition, the cleaning robot can be reduced in sizewhile maintaining the sizes of the battery, the dust box, the suctionblower, and the like. When the size of the cleaning robot is reduced,power consumption is suppressed, and a narrower gap can be cleaned.

The gear case 7 preferably includes an arc-shaped or substantiallyarc-shaped upper portion 71 and a flat bottom portion 72 which extendsin a horizontal or substantially horizontal direction. When viewed inthe axial direction as in FIG. 6, the upper portion 71 of the gear case7 is preferably positioned slightly inward from the ground surface 621of the wheel 6, and extends in the arc shape along the ground surface621. On the other hand, the bottom portion 72 of the gear case 7 ispreferably disposed at a high position closer to the lower side of thefinal gear 5. Accordingly, the gear case 7 is disposed at a positionbiased toward the upper side with respect to the wheel 6. In addition, aspace with no member being disposed therein is ensured between thebottom portion 72 of the gear case 7 and the ground. Accordingly,contact between the gear case 7 and the ground during traveling is lesslikely to occur.

In addition, the gear case 7 of this preferred embodiment preferablyincludes a plate-shaped rib 73 which protrudes in the axial directionfrom the surface in the vicinity of the bottom portion 72 on the inputside. In addition, the motor 2 is disposed above the rib 73. When thewheel unit 1 of this preferred embodiment is attached to the cleaningrobot, the rib 73 is fixed to a frame body of the cleaning robot by ascrew or the like, for example.

When viewed in the axial direction as in FIGS. 3 and 6, the gear case 7of this preferred embodiment does not protrude in a specific directionfrom the ground surface of the wheel 6. Therefore, the wheel units 1having the same structure can be reversely arranged on the left and theright of the cleaning robot. There is no need to change the design ofthe wheel unit 1 on the left side and the right side of the cleaningrobot, and thus the number of manufacturing processes and themanufacturing cost of the cleaning robot are reduced.

In addition, in this preferred embodiment, the diameters of all of thesmall-diameter gear portions 413, 423, and 433 of the three compositegears 41 to 43 are preferably smaller than the diameter of the rotatingportion 22 of the motor 2. In addition, in this preferred embodiment,the sum of the diameter of any of the large-diameter gear portions 412,422, and 432 of the three composite gears 41 to 43 and the diameter ofthe final gear 5 is preferably greater than the radius of the groundsurface 621 of the wheel 6. When the diameter of the rotating portion 22of the motor 2 is large, high torque can be generated by using themagnet 221 having a large diameter. On the other hand, when thediameters of the large-diameter gear portions 412, 422, and 432 arelarge and the diameters of the small-diameter gear portions 413, 423,and 433 are small, a reduction gear ratio of the speed reductionmechanism 4 is increased. Accordingly, the torque is further increased.

In addition, even in a case where the composite gears to 43 are made ofa resin, when the diameters of the composite gears 41 to 43 are designedto be large, high durability can be obtained.

As described above, in the wheel unit 1, the portion of the final gear 5is positioned on the inside of the cylindrical or substantiallycylindrical area surrounded by the ground surface 621 of the wheel 6.This structure is excellent because the dimensions of the wheel unit 1in the axial direction can be reduced, but has a problem in that it isdifficult for the support structure of the rotation support portion 81with respect to the gear case 7 to be widened in the axial direction.

Considering this, in the wheel unit 1, the outside diameter of therotation support portion 81 is greater than the outside diameter of thefinal gear support shaft 51. Accordingly, a large contact portionbetween the rotation support portion 81 and the circular hole portion 70of the gear case 7 can be obtained. Therefore, a surface pressure in asliding portion of the outer peripheral surface of the rotation supportportion 81 and the circular hole portion 70 of the gear case 7 ispreferably reduced, and the wear of the sliding portion is furtherreduced. As a result, in the support structure of the rotation supportportion 81 with respect to the gear case 7, high durability is obtained.

Third Preferred Embodiment

Subsequently, a wheel unit 1B according to a third preferred embodimentof the present invention will be described with a focus on thedifferences from the second preferred embodiment.

FIG. 7 is a side view of the wheel unit 1B according to the thirdpreferred embodiment. FIG. 8 is a side view of the wheel unit 1B, inwhich a gear case 7B is cut-away for illustration purposes. Similarly tothe second preferred embodiment, the wheel unit 1B preferably includes amotor 2B, a pinion gear 3B, a speed reduction mechanism 4B, a final gear5B, a wheel 6B, and the gear case 7B. When the motor 2B is driven, thedrive force of the motor 2B is transmitted to the wheel 6B via thepinion gear 3B, the speed reduction mechanism 4B, and the final gear 5B.Accordingly, the wheel 6B is rotated.

As illustrated in FIG. 8, in this preferred embodiment, among threecomposite gears 41B to 43B defining the speed reduction mechanism 4B,the first composite gear 41B is preferably supported by a final gearsupport shaft 51B which supports the final gear 5B. That is, the firstcomposite gear 41B and the final gear 5B are supported by the commonfinal gear support shaft 51B. The final gear support shaft 51B is fixedto the gear case 7B so as not to rotate. The first composite gear 41Band the final gear 5B preferably independently rotate about the finalgear support shaft 51B.

In this manner, when the support shaft of at least one composite gearincluded in the speed reduction mechanism and the support shaft of thefinal gear are used in common, the plurality of gears are more compactlyarranged in the inner portion of the gear case 7.

FIGS. 9 and 10 are side views of the wheel unit 1B attached to acleaning robot 9B. The cleaning robot 9B preferably includes a pair ofsuspension mechanisms 91B which impel the wheel unit 1B toward the lowerside. The pair of suspension mechanisms 91B are arranged in the movementdirection. Each of the suspension mechanism 91B

includes an elastic member 911B which elongates and contractsvertically.

The gear case 7B preferably includes a pair of receiving portions 74Bwhich protrude forward in the movement direction and rearward in themovement direction. Lower end portions of the pair of elastic members911B abut on the upper surfaces of the receiving portions 74B. Inaddition, through-holes 741B that extend vertically are preferablydefined in the pair of receiving portions 74B. A guide shaft 912B thatextends vertically is inserted into the through-hole 741B.

During the traveling of the cleaning robot 9B, the pair of elasticmembers 911B elastically elongate and contract in response to anexternal force. Therefore, the wheel unit 1B is vertically movedrelative to the frame body of the cleaning robot 9B. Accordingly, thecleaning robot 9B stably travels on ground having unevenness.

In this preferred embodiment, the plurality of gears are arranged sothat the speed reduction mechanism 4B and the final gear 5B which arearranged in the inner portion of the gear case 7B and the through-hole741B of the receiving portion 74B do not overlap each other. That is, asdescribed above, the first composite gear 41B and the final gear 5B aresupported by the common final gear support shaft 51B. In addition, thefirst composite gear 41B and the second composite gear 42B arepreferably arranged in or substantially in the vertical direction. As aresult, the dimensions of both the speed reduction mechanism 4B and thefinal gear 5B in the movement direction are reduced. Accordingly, thespeed reduction mechanism 4B, the final gear 5B, and the through-hole741B of the receiving portion 74B are preferably arranged withoutoverlapping each other.

In this preferred embodiment, the suspension mechanisms 91B arepreferably defined by the pairs of receiving portions 74B included inthe wheel unit 1B, and the elastic members 911B and the guide shafts912B provided in the cleaning robot 9B. However, by assembling theelastic members and the guide shafts into the wheel unit, the wheel unititself may include the complete suspension mechanisms.

Fourth Preferred Embodiment

FIG. 12 is a side view of a wheel unit 1D according to a fourthpreferred embodiment of the present invention. FIG. 13 is across-sectional view of the wheel unit 1D viewed in a case where a gearcase 7D is cut-away in a plane including a final gear support shaft 51Dand the center of a second gear support shaft for illustration purposes.The wheel unit 1D preferably includes a motor (not shown), a pinion gear3D, a speed reduction mechanism 4D, a final gear 5D, a wheel 6D, and agear case 7D, and a rotation support portion 81D is provided between thefinal gear 5D and the wheel 6D. When the motor 2D is driven, the driveforce of the motor 2D is transmitted to the wheel 6D via the pinion gear3D, the speed reduction mechanism 4D, and the final gear 5D.Accordingly, the wheel 6D is rotated.

As illustrated in FIG. 13, in this preferred embodiment, among threecomposite gears 41D to 43D defining the speed reduction mechanism 4D,the first composite gear 41D is preferably supported by the final gearsupport shaft 51D which supports the final gear 5D. That is, the firstcomposite gear 41D and the final gear 5D are preferably supported by thecommon final gear support shaft 51D. The final gear support shaft 51D ispreferably supported by a final gear support shaft support portion 54Dso as not to rotate with respect to the gear case 7D.

The first composite gear 41D and the final gear 5D rotate about thefinal gear support shaft 51D at different speeds.

Accordingly, when the support shaft of at least one composite gearincluded in the speed reduction mechanism and the support shaft of thefinal gear are used in common, the plurality of gears are furthercompactly arranged in the inner portion of the gear case 7D.

The gear case 7D preferably includes an annular sleeve member 70D, asleeve holding portion 77D which preferably includes a cylindrical innerperipheral surface, and an annular stopper plate portion 78D whichextends inward in the radial direction over the inner peripheralsurface. The sleeve member 70D is preferably disposed coaxially with thefinal gear support shaft 51D, and the outer peripheral surface of thesleeve member 70D comes into contact with the inner peripheral surfaceof the sleeve holding portion 77D and a surface of the stopper plateportion 78D on the output side. In this configuration, the sleeve member70D is further stably held.

At a position of the final gear 5D adjacent to the output side, therotation support portion 81D which rotates while being supported by thegear case 7D is preferably provided. The rotation support portion 81D ispositioned between the final gear 5D and the wheel 6D, and the innerperipheral surface of the sleeve member 70D comes into contact with theouter peripheral surface of the rotation support portion 81D with alubricant interposed therebetween.

In addition, the outside diameter of the rotation support portion 81D ispreferably greater than the outside diameter of the final gear supportshaft 51D. In this configuration, a large contact portion of therotation support portion 81D and the sleeve member 70D is ensured. As aresult, a surface pressure in a sliding portion of the outer peripheralsurface of the rotation support portion 81D and the circular holeportion 70D of the gear case 7 is reduced, and the wear of the slidingportion is further reduced. As a result, the wear is reduced, and in thesupport structure of the rotation support portion 81D, good durabilityis obtained.

The final gear 5D and the rotation support portion 81D are preferablyportions of a single monolithic member made of a continuous material,and are molded by a resin injection molding method, for example. In thiscase, the number of components is reduced, and thus assembly of thewheel unit 1D is facilitated.

The final gear 5D includes outer teeth 52D in which a plurality of teethare aligned in a peripheral direction and an inner cylindrical portion53D which is cylindrical and is disposed on the inside of the outerteeth 52D in the radial direction. An end portion of the innercylindrical portion 53D on the input side is positioned closer to theinput side than an end portion of the outer teeth 52D on the input side.The final gear support shaft 51D is accommodated on the inside of theinner cylindrical portion 53D in the radial direction, and a gap isprovided between an end portion of the final gear support shaft 51D ison the output side and the inner cylindrical portion 53D.

In addition, a tooth root diameter (dr in FIG. 13) of the final gear 5Dis preferably greater than the outside diameter of the rotation supportportion 81D. Furthermore, the outer peripheral surface of the sleevemember 70D is preferably larger than the tooth root diameter. In thisconfiguration, the final gear 5D is less likely to come into contactwith the gear case 7D. In addition, this configuration is also effectivein ensuring a place for disposing a sleeve contact surface 56D, whichwill be described later.

An end surface of the sleeve member 70D on the input side preferablyincludes an annular convex portion 701D. The annular convex portion 701Dcan come into contact with the sleeve contact surface 56D which isprovided on the output side of the final gear 5D. That is, thedimensions of each portion of the final gear 5D and the first compositegear 41D are expected to have “play”, and in a state where the gears arepressed from the other side in the axial direction, that is, from theupper side of the figure, the annular convex portion 701D comes intocontact with the sleeve contact surface 56D. However, since the shape ofthe contact portion is convex and the contact area is small, africtional force due to the contact is relatively small.

In addition, in the claims of the present invention, the expression“come into contact” is used, but actually means “be in a state capableof coming into contact” as described above. Bearings always have acertain degree of play, and each portion of the gears is moved in arange of the play such that each portion can be in a state of cominginto contact with or in a state of not coming into contact with adjacentmembers. However, in such a case, each portion of the gear mechanismsneeds to be designed and manufactured on the premise that the portionsthereof can come into contact with each other. Therefore, although itcannot be said that portions come into contact with each other when theyhave a dimensional relationship in which they actually can come intocontact with each other, in the descriptions of preferred embodiments ofthe present invention, in a case where the portions can come intocontact with each other in the range of the play of the bearings, theexpressions “come into contact” and “be in contact” are used.

In addition, an annular first thrust washer 54D which surrounds thefinal gear support shaft 51D is interposed between the end portion ofthe inner cylindrical portion 53D on the output side and the end portionof the first composite gear 41D on the output side in the axialdirection. In this configuration, wear due to the contact between thefinal gear 51D and the first composite gear 41D, which rotate atdifferent speeds, is significantly reduced.

The final gear support shaft support portion 79D is preferably providedin the gear case 7D, and the final gear support shaft 51D is supportedby the final gear support shaft support portion 79D. The upper end ofthe final gear support shaft 51D is positioned between the sleeveholding portion 77D and the upper end and the lower end of the sleevemember 70D in the axial direction. With this unique configuration, theupper end of the final gear support shaft 51D is indirectly supported bythe sleeve holding portion 77D. Therefore, although the upper end is afree end, the final gear support shaft 51D is stably held by the gearcase 7D.

In addition, between the final gear support shaft support portion 79Dand the end portion of the first composite gear 41D on the input side,an annular second thrust washer 55D which surrounds the final gearsupport shaft 51D is preferably interposed. In the configuration, weardue to the contact between the gear case 7D and the first composite gear41D is significantly reduced.

Modified Example of a Preferred Embodiment

While the exemplary preferred embodiments of the present invention havebeen described above, the present invention is not limited to theabove-described preferred embodiments.

For example, as a wheel unit 1C of FIG. 11, a motor cover 75C whichaccommodate a motor 2C may be attached to a gear case 7C. In thisexample, the motor 2C is preferably fixed to an attachment plate 76Cwhich is a partition wall interposed between the gear case 7C and themotor cover 75C. Accordingly, the motor 2C is firmly fixed to the gearcase 7C. In addition, a rotating portion 22C of the motor 2C is reliablyprevented from coming into contact with another member in the cleaningrobot, waste from the outside, or a person.

The number of composite gears included in the speed reduction mechanismmay be three as in the above preferred embodiments, and mayalternatively be two or four or more. However, in order to obtain hightorque while using a small motor, three or more composite gears may beused. In addition, a large-diameter gear portion and a small-diametergear portion of the composite gear may be prepared as separate membersand be fixed to each other.

The support shaft of each composite gear may be supported to rotaterelative to the gear case. In this case, the support shaft and thecomposite gear may be fixed to each other so that the composite gearrotates along with the support shaft. In addition, the final gearsupport shaft may be supported to rotate relative to the gear case. Inthis case, the final gear support shaft, the final gear, the rotationsupport portion, and the wheel may be fixed so that the final gear, therotation support portion, and the wheel rotate along with the final gearsupport shaft.

In order to reduce the dimensions of the wheel unit in the axialdirection, on the inside of the cylindrical or substantially cylindricalarea surrounded by the ground surface of the wheel, at least a portionof the final gear may be disposed. The entire final gear may be disposedon the inside of the area. In addition, not only the final gear, butalso the composite gear may be disposed on the inside of the area.

The support structure of the rotation support portion with respect tothe gear case may be a bearing structure other than the slide bearing.For example, between the rotation support portion and the circular holeportion of the gear case, a ball bearing may be provided. However, as inthe above preferred embodiments, when the slide bearing is used, thesupport structure of the rotation support portion with respect to thegear case is realized with a smaller number of components.

The bottom surface of the gear case may be a flat surface as in FIG. 6,may be a curved surface as in FIG. 8, and may be any other desirableshape. However, in order to dispose the gear case at a position biasedtoward the upper side with respect to the wheel, the bottom surface ofthe gear case may be a curved surface having a

larger radius of curvature than the ground surface of the wheel or aflat surface.

In addition, another member may be interposed between the membersdefining the final gear and the wheel. That is, the members defining thefinal gear may be fixed to the wheel via another member interposedtherebetween.

A gap which is equal to or smaller than the play in the axial directionmay be provided between the annular convex portion 701D of the sleevemember 70D and the sleeve contact surface 56D which is provided on theoutput side of the final gear 5D, if so desired.

In this case, since the final gear 5D is rotatably supported by thefinal gear support shaft 51D, movement thereof in the axial direction ispossible, and according to the movement of the final gear 5D in theaxial direction, the sleeve contact surface 56D may be in a state ofcoming into contact with the circular convex portion 701D.

In addition, considering the required size and torque, the wheel unit ofthe preferred embodiments of the present invention is particularlyappropriate for a domestic cleaning robot, but may also be used for anyother electric appliances. For example, the wheel unit may be used in arobot for conveying goods or a toy which is wirelessly controlled. Inaddition, indoors or outdoors, the wheel unit may be used in an electricwheelchair which travels with a person riding thereon. In addition, thewheel unit according to preferred embodiments of the present inventionmay be used in domestic electric appliances, and may also be used inapparatuses for business use.

In addition, elements described in the preferred embodiments and themodified example described above may be appropriately combined in arange with no contradictions.

Preferred embodiments of the present invention may be used, for example,in a wheel unit.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. A wheel unit, comprising: a motor including amotor shaft; a pinion gear which is fixed to a rotating portion of themotor; a wheel which includes an annular ground surface and rotatesaround a final gear support shaft; a final gear made of a resin, fixedto the wheel directly or via another member and disposed on one side inan axial direction with respect to the wheel; a speed reductionmechanism which decelerates rotation of the pinion gear and transmitsthe rotation to the final gear; a gear case which accommodates thepinion gear, the speed reduction mechanism, and the final gear; and arotation support portion which rotates along with the final gear and thewheel while being supported by the gear case directly or via anothermember and is provided between the final gear and the wheel; whereinwhen viewed from one side in the axial direction, the final gear supportshaft and the motor shaft are disposed in different positions; the motorincludes a rotor magnet on an outside of an armature in a radialdirection; at least a portion of the final gear is positioned on aninside of a cylindrical or substantially cylindrical area surrounded bythe ground surface; the speed reduction mechanism includes a pluralityof composite gears each including a large-diameter gear portion and asmall-diameter gear portion; an initial stage composite gear is disposedon the one side of the final gear in the axial direction, and thelarge-diameter gear portion of the initial stage composite gear mesheswith the pinion gear; the initial stage composite gear is supported bythe final gear support shaft; and the initial stage composite gear andthe final gear are rotatable relative to the gear case.
 2. The wheelunit according to claim 1, wherein the gear case includes an annularsleeve member which is disposed coaxially with the final gear supportshaft; and an outer peripheral surface of the rotation support portioncontacts with an inner peripheral surface of the sleeve member withlubricant interposed therebetween; and a tooth root diameter of thefinal gear is greater than an outside diameter of the rotation supportportion; an outer peripheral surface of the sleeve member is larger thanthe tooth root diameter; the gear case includes: a cylindrical sleeveholding portion which surrounds the rotation support portion; and anannular stopper plate portion which extends inward in a radial directionfrom a portion of the sleeve holding portion on the other side in theaxial direction; wherein the sleeve member contacts with an innerperipheral surface of the sleeve holding portion and a surface of thestopper plate portion on the one side in the axial direction.
 3. Thewheel unit according to claim 2, wherein the sleeve member includes anannular convex portion in an end surface thereof on the one side in theaxial direction; the final gear includes an annular sleeve contactsurface directed toward the other side in the axial direction; and theannular convex portion contacts with the sleeve contact surface.
 4. Thewheel unit according to claim 3, wherein the final gear and the rotationsupport portion are portions of a single monolithic rotation member madeof a resin.
 5. The wheel unit according to claim 1, wherein the gearcase includes a circular hole portion including a cylindrical innerperipheral surface which supports the rotation support portion; and theinner peripheral surface of the circular hole portion of the gear casecontacts with an outer peripheral surface of the rotation supportportion with a lubricant interposed therebetween.
 6. The wheel unitaccording to claim 5, wherein an outside diameter of the rotationsupport portion is greater than an outside diameter of the final gearsupport shaft.
 7. The wheel unit according to claim 1, wherein all ofthe plurality of composite gears are positioned on an inside of acylindrical surface on which the ground surface of the wheel isprojected in a direction of the final gear support shaft; and anentirety of the final gear is positioned on an inside of the cylindricalor substantially cylindrical area surrounded by the ground surface. 8.The wheel unit according to claim 1, wherein the motor includes astationary portion and a rotary portion which rotates relative to thestationary portion, and the stationary portion is fixed to the gearcase.
 9. The wheel unit according to claim 8, wherein an axial dimensionof the motor is smaller than a diameter of the rotary portion of themotor.
 10. The wheel unit according to claim 9, wherein the rotaryportion of the motor rotates together with the axially extending motorshaft, and an end portion on the output side of the motor shaft extendsinto an inner side of the gear case.
 11. The wheel unit according toclaim 1, wherein the motor includes a stationary portion and a rotaryportion which rotates relative to the stationary portion, and the motoris fixed to an attachment plate.
 12. The wheel unit according to claim11, wherein the attachment plate is interposed between the gear case andthe motor cover, and defines a partitioning wall.
 13. The wheel unitaccording to claim 1, wherein the gear case includes a bottom surfacewhich includes a flat surface or a curved surface which has a biggercurvature radius than the ground surface of the wheel, and the motor isdisposed on an upper side above the bottom surface.
 14. The wheel unitaccording to claim 13, wherein the gear case includes a plate-shaped ribwhich axially protrudes from a surface on the input side in vicinity ofor adjacent to the bottom surface, and the motor is disposed above therib.
 15. The wheel unit according to claim 14, wherein the gear caseincludes an upper portion which expands in an arcuate shape along theground surface of the wheel, and the motor is disposed on a lower sidebelow an upper end of the upper portion.
 16. The wheel unit according toclaim 15, wherein the gear case is provided with a motor cover whichaccommodates the motor.
 17. The wheel unit according to claim 16,further comprising: a motor cover which accommodates the motor; and apartition wall which is interposed between the gear case and the motorcover; wherein the motor is fixed to the partition wall.